gh-142353: Isolate tests from personal GNU Readline init files

[johnslavik]

CC @ZeroIntensity skip news, needs backport to 3.13, needs backport to 3.14

• Issue: Readline-reliant tests are not isolated from personal init files #142353

spam review

[johnslavik]

I'll simplify this a bit, thanks for a quick review!

[vstinner]

LGTM

[miss-islington-app]

Thanks @johnslavik for the PR, and @vstinner for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14.
🐍🍒⛏🤖

[bedevere-app]

GH-142634 is a backport of this pull request to the 3.14 branch.

[bedevere-app]

GH-142635 is a backport of this pull request to the 3.13 branch.

[vstinner]

Merged, thanks for the fix.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Windows11 Refleaks 3.13 (tier-1) has failed when building commit e7bb732.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1484/builds/902) and take a look at the build logs.
4. Check if the failure is related to this commit (e7bb732) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1484/builds/902

Failed tests:

• test_httpservers

Failed subtests:

• test_large_content_length_truncated - test.test_httpservers.CGIHTTPServerTestCase.test_large_content_length_truncated

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "b:\uildarea\3.13.ware-win11.refleak\build\Lib\test\libregrtest\single.py", line 201, in _runtest_env_changed_exc
    return
ResourceWarning: unclosed <socket.socket fd=720, family=2, type=1, proto=0, laddr=('127.0.0.1', 53869), raddr=('127.0.0.1', 53868)>


Traceback (most recent call last):
  File "b:\uildarea\3.13.ware-win11.refleak\build\Lib\test\libregrtest\single.py", line 201, in _runtest_env_changed_exc
    return
ResourceWarning: unclosed <socket.socket fd=688, family=2, type=1, proto=0, laddr=('127.0.0.1', 49650), raddr=('127.0.0.1', 49649)>


Traceback (most recent call last):
  File "b:\uildarea\3.13.ware-win11.refleak\build\Lib\test\test_httpservers.py", line 1028, in test_large_content_length_truncated
    res = self.request('/cgi-bin/file1.py', 'POST', b'x', headers)
  File "b:\uildarea\3.13.ware-win11.refleak\build\Lib\test\test_httpservers.py", line 88, in request
    self.connection.request(method, uri, body, headers)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "b:\uildarea\3.13.ware-win11.refleak\build\Lib\http\client.py", line 1358, in request
    self._send_request(method, url, body, headers, encode_chunked)
    ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "b:\uildarea\3.13.ware-win11.refleak\build\Lib\http\client.py", line 1404, in _send_request
    self.endheaders(body, encode_chunked=encode_chunked)
    ~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "b:\uildarea\3.13.ware-win11.refleak\build\Lib\http\client.py", line 1353, in endheaders
    self._send_output(message_body, encode_chunked=encode_chunked)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "b:\uildarea\3.13.ware-win11.refleak\build\Lib\http\client.py", line 1152, in _send_output
    self.send(chunk)
    ~~~~~~~~~^^^^^^^
  File "b:\uildarea\3.13.ware-win11.refleak\build\Lib\http\client.py", line 1077, in send
    self.sock.sendall(data)
    ~~~~~~~~~~~~~~~~~^^^^^^
ConnectionAbortedError: [WinError 10053] An established connection was aborted by the software in your host machine